Ceramic packing element

ABSTRACT

The invention provides an improved ceramic bed limiter packing element having a uniform cross-section in the length direction with the basic shape of a bow-tie and having a plurality of through passages parallel to the length dimension.

BACKGROUND OF THE INVENTION

[0001] This invention relates to packing elements of the type that are often called “random” or “dumped” packings. Such packings are used to fill towers units in which mass or heat transfer processes occur. A particularly important application is the use of such ceramic elements in heat recovery operations where it is necessary to provide maximum effective contact with hot fluids passing through the reactor. Another key factor in maximizing efficiency is the maintenance of as low a pressure difference between top and bottom of the tower as possible. To ensure this the packing elements should present the minimum resistance to flow. This is promoted by very open structures but open structure alone is of limited use if the elements in the tower nest together such that parts of one packing element penetrate within the space of a second element. It is therefore important that the design of the elements minimize the tendency of the elements to nest together. Another particularly important application is as a bed topping material which is intended to keep material within a bed confined with limited ability to be entrained in a gas flow or to be caused to move around by such a flow. Such entrainment or abrasion typically causes significant losses to the material in the bed.

[0002] The present invention relates particularly to ceramic packing elements that are produced by an extrusion or a dry-pressing process and hence have an essentially uniform cross-section along one axial direction which provides an axis of symmetry for the element. Several such shapes have been described in the art ranging from the very simple to the complex. All are based on an essentially cylindrical shape and differ basically in the internal structure within the cylindrical shape. The simplest structure is a basic cylinder with no internal structure at all. This type of structure is often called a Raschig ring and has been known for many years. At the other end of the complexity scale are the structures described in U.S. Design Pat. No. 455,029 and U.S. Pat. No. 6,007,915. Between the extremes there are simple wagon-wheel shapes such as are described in U.S. Pat. Nos. 3,907,710 and 4,510,263. Others show deformed cylindrical structures such as those described in U.S. Pat. No. 5,304,423.

[0003] For certain applications, such as bed limiters, the pressure drop is less important since the thickness of the bed limiter layer is relatively small. It is far more important that the packing elements do not nest together and still allow free passage of gases while being heavier that the elements comprising the bed on which the packing elements rest and whose extent is thereby limited

DESCRIPTION OF THE INVENTION

[0004] The present invention provides a solid ceramic packing element having an essentially uniform cross-section along an axis of symmetry in the direction of extrusion defining the length of the element and first and second concave external surfaces at the ends of height and width axes respectively perpendicular to the length direction, said concave surfaces being connected by convex surfaces, and the element being provided with at least four through passages in the length direction.

[0005] The provision of an essentially uniform cross-section along the direction defining the length of the element does not preclude the provision of ends to the element that are not perpendicular to the length direction. Indeed it is often preferred that the ends be cut at an angle to the length direction since this is found to reduce the incidence of “nesting” or alignment of the elements in a manner that increases the pressure drop across a reactor containing the elements. The ends can also be cut to have concave, convex, or dentate appearances in cross-section.

[0006] Alternatively the element can be formed by a pressing or molding process in which case relatively small intermediate flat surfaces may be included on the exterior surfaces at the junction between the concave and convex surfaces to facilitate easy handling of the product during forming. The intermediate flat surfaces are short relative to the concave and convex surfaces and are intended merely to facilitate handling in a production process in which the elements are molded rather than extruded.

[0007] In a preferred element of the invention, the width and height dimensions of the element are unequal with the ratio of width to height being from 1.25:1 to 3:1 and more preferably from about 1.3:1 to 2.0:1. Thus, in visual terms, the cross-section perpendicular to the length of the preferred elements of the invention resembles the classic “dog-bone” or “bow tie” shape.

[0008] The length dimension is preferably less than the width with the preferred width to length ratio being from 1.5:1 to 5:1 and more preferably from 1.5:1 to 4:1.

[0009] There are at least three passages through the element and the preferred number can be anything from 4 to 275 and preferably from 7 to 20. The passages through the element are preferably uniformly spaced and can have any desired cross-section. However since the purpose of the passages is to reduce the pressure drop across a bed comprising the elements, round cross-sections are preferred. Clearly the larger the number of passages the smaller the cross-section must be. It is preferred therefore that the cross-section of the passages does nor exceed one half the smallest dimension of the element and is more preferably not greater than one third of this dimension. For practical reasons it is often preferred that the passages are identical in dimensions and are round. In the cross-section of the packing element, the area represented by the passages can be from 20 to 75% and more preferably from 40 to 67%, of the total cross-section of the element.

[0010] The element is conveniently extruded from a ceramic material and this is understood to embrace ceramic materials such as for example those based on aluminosilicate clays, alumina, zirconia, cordierite, titania, alone or in admixture with one another or other ceramic-forming components.

[0011] In addition to use the use as a bed limiter or as a regular packing element providing mass transfer surfaces, it is possible to provided that the element has a porous construction making it suitable for use also as carrier for a catalyst deposited within the pores of the element as well as within the through passages of the element. It is possible therefore to provide for a catalyst bed comprising conventional porous catalyst-on-carrier components and limit that bed with elements according to the invention that not only provide the bed-limiting function but also serve to react with any remaining reactants that were not converted during passage through the portion of the bed containing the catalyst-bearing components.

[0012] It is foreseeable that elements with the design features described above and having bed-limiting functions could be provided by elements made from plastic materials rather than ceramics.

DRAWINGS

[0013]FIG. 1 is a cross-section of a bed limiter packing element of the invention.

[0014]FIG. 2 is a cross-section of a similar element to that shown in FIG. 1 except for the provision of flat exterior portions connecting the convex and concave portions.

[0015] FIGS. 3(a to d) shows four different side views illustrating possible end configurations of the element.

DESCRIPTION OF PREFERRED EMBODIMENT

[0016] The invention is now more particularly described with reference to the embodiment illustrated in FIG. 1. This is not intended to imply any necessary limitations in the scope of the invention because it will be readily appreciated that many minor variations could be made without departing from the essential spirit of the invention.

[0017] In FIG. 1 a bed limiter packing element, 1, is shown in cross-section along the length dimension. The element has a width dimension, W, and a height dimension, H, with the W:H ratio being about 1.5:1. At either end of the height dimension are first concave surfaces, 2, and at either end of the width dimension are second concave surfaces, 3. These first and second concave surfaces are connected by convex surfaces, 4. Since the element has a uniform cross-section along its length the concave surfaces can be regarded as channels in the outside surface of the element running the length of the element. A plurality of passages, 5, run through the element parallel to the length dimension. The passages are preferably round in cross-section and in the illustrated element have the same diameter, which represents about one third of the height dimension.

[0018] In the embodiment of FIG. 2 small flat exterior surfaces, 6, connect the concave and convex sections. The shape is however otherwise the same.

[0019] In FIG. 3 four optional ways of forming the ends of the elements are shown. In FIGS. 3a to 3 d the drawing shows, (for left and right ends respectively in each case), concave and straight-cut ends; two dentate-cut ends; two concave ends; and dentate and concave ends. 

What is claimed is:
 1. A ceramic packing element having an essentially uniform cross-section along an axis passing through the center of the element and about which the element is symmetrical defining the length of the element, and first and second concave external surfaces at the ends of height and width axes respectively perpendicular to the length direction, said concave surfaces being connected by surfaces that are selected from convex surfaces and convex surfaces connected to the concave surfaces by relatively short intermediate flat surfaces, and the element being provided with at least three through passages in the length direction.
 2. An element according to claim 1 in which the concave surfaces are connected directly to convex surfaces.
 3. An element according to claim 1 in which the width and height dimensions of the element are unequal with the ratio of width to height being from 1.25:1 to 3:1.
 4. An element according to claim 2 in which the width and height dimensions of the element are in a ratio of from about 1.3:1 to 2.0:1.
 5. An element according to claim 1 in which the ratio of the width to the length is from 1.5:1 to 5:1.
 6. An element according to claim 1 in which the element is provided with from 3 to 275 passageways.
 7. An element according to claim 5 in which the passageways are round in cross-section and the diameter of each is less than one half of the height of the element.
 8. An element according to claim 5 in which the passageways have identical dimensions.
 9. An element according to claim 1 in which the total cross-sectional are of the passages represents from 20 to 75% of the total cross-sectional area of the element.
 10. An element according to claim 1 in which the ceramic is a porous material. 